a) b - École Polytechnique de Montréal

with a polyelectrolyte(Jaffar et al., 2004). In the LbL approach, the adsorption process involves
consecutive and alternate deposition of polyelectrolytes including polyanions and polycations
driven by electrostatic forces, or other interactions such as hydrogen bonding. Although
oppositely charged polyelectrolyte side groups represent a quite powerful attraction, some other
types of intermolecular interactions between polyelectrolytes such as van –der Waals, dipole-
dipole, and ion-dipole, involve chains of polyelectrolyte and molecules of solvent.
Polyelectrolytes or polysalts are similar to both high molecular weight compounds (polymers)
and electrolytes (salts). This means that due to electrolyte groups, they are electrically
conductive in aqueous solutions and because of macromolecules, their solutions are viscous. In
the LbL technique, each step involves dipping of the substrate into an oppositely-charged
solution followed by a rinsing step with water. To maintain film growth until the desired
thickness or number of bilayers is achieved, alternate dipping is repeated. A stepwise increase of
multilayer thickness or film mass with each deposition step is expected. Thickness of each
monolayer in this method is dictated by the polymer geometry; also supramolecular structures of
alternately charged polymers can be controlled by polymer combination, surface charges, and
solution parameters(Decher, 1997). The thickness increment after each deposition, referred to as
growth rate, shows a steady state regime of multilayer assembly with several nanometers
thickness for each layer.
Decher(Decher & Schlenoff, 2003) mentioned two significant advantages for layer-by-layer
assembly method: 1) surface properties of existing objects and devices can be controlled by
controlling surface functionality, and 2) thin-film devices can be fabricated in a very controlled
way by template-assisted assembly. Properties of devices can be engineered by controlling the
spatial arrangement of functionality in multimaterial-layered nanocomposites. There are some
more advantages for this technique in comparison with other methods such as its low-cost
preparation and its environmentally friendliness. Kotov(Kotov, Dekany, & Fendler, 1995) added
that by varying the total number of deposited layers, the total thickness of the coating can be
controlled with a precision of a few nanometers. Thus, the technique is exceptionally simple,
precise, versatile and scale-up friendly.
After showing the deposition of oppositely charged polymer layers, the number of published
papers on polyelectrolyte multilayer has grown exponentially. More than 200 published papers
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